The present invention relates to an apparatus for imaging particles in a liquid flow, and in particular to an imaging flow cytometer for imaging and analyzing particle components in a sample liquid containing particle components such as blood and urine, or fine particles such as organic high polymer particles in suspension, or the like, and more particularly to an imaging flow cytometer capable of obtaining a clear still image of particles flowing at high speed (for example, 5 m/sec. or more) even with a light source of a long light emission time such as a lamp, by using an image intensifier with a high speed gate function, in a flow cytometer with still imaging function.
To image particles in a sample liquid flowing at a high speed of several meters per second in a flow cell, using a flow cytometer, as conventionally shown in FIG. 1, it is generally know to capture a particle image free of vibration, by the combination of a pulse laser light source 29 capable of emitting an intense light only for a moment and a video camera 43. In a flow cell 14, a sheath flow 15 is formed by passing sheath liquid around the sample flow including the particles 16 to be detected, and this sample fine flow 15 is illuminated with laser light from an argon laser generator 10. The light signal (the scattered light or fluorescent light) from the particle is detected by a light detector (photomultiplier or the like) 22, and a signal S1 is sent to a signal processing unit 24 to be processed, thereby analyzing the particles. The sheath flow is a flow covered with a laminar sheath liquid around the suspension of particles in order to pass the particles neatly in one row precisely in the middle of the liquid flow. Also shown in FIG. 1 is a pulse emission trigger signal S4, a laser power supply 27, an image processing unit 46, condenser lenses 12, 31, objective lenses 20, 33, a projection lens 41, and a beam stopper 18.
In the Japanese Laid-open Patent Sho. 62-254037, it is disclosed to image only particles with specific characteristics, by detecting the particles by the image pickup device nearly simultaneously, by providing the flow cytometer with a streak image pickup device, and processing the imaging signal only when matched with a predetermined characteristic value. It is also disclosed to use a high sensitivity camera and a camera tube as the image pickup device, and picture the entire image instantly.
The Japanese Laid-open Patent Sho. 63-94156 discloses a flow cytometer in which the light source for detecting particles is always illuminated, passing of a cell is detected by a cell detector, and after delaying for a specific time in a delay circuit, the light source for the laser pulse for imaging is turned on to picture the cell.
In the conventional particle imaging flow cytometer shown in FIG. 1, since the laser light source possesses a high coherence, the interference fringe is often obvious in the obtained particle image, so that the image quality is not so high. Besides, since the laser light source presents a monochromatic light, a color image of the particles is not obtained. Besides, the pulse laser light source, of the gas type, is large in size, and the power source is also large in scale, and is very expensive.
By using a xenon flash lamp small in coherence as the light source, a clear image without an interference fringe may be obtained, but the luminous time of the xenon flash lamp is generally long, 1 .mu.sec. or more, and in this case the image may deviate unless the sheath flow velocity is 0.3 m/sec. or less. At the flow velocity of 0.3 m/sec., however, the intrinsic high processing ability of the flow cytometer, that is, the large number of cells analyzed per unit of time is not achieved.
Besides, neither publication refers to imaging of still pictures of particles by using an image intensifier with high speed gate, which is a feature of the present invention.